Packet communications network and communications method

ABSTRACT

A packet communications network for transmitting data between nodes by the use of cell slots circulating the network includes a center node inserted in the ring network for sequentially generating, at a selected rate, first and second types of cell slots interleavingly for transmitting first and second types of data, respectively. Each cell slot has a type code for identifying either one of the first and second types, and a status code for identifying the different status of the cells. Each node detects whether the received cell is the first type or the second type. If the received cell is the first type, it is used for transmitting the connection-oriented data under MARS system. If the received cell is the second type, it is used for transmitting the connectionless data under ATMR system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ATM (asynchronous transfer mode)ring network for standardized communication of multimedia information,and specifically to a ring packet communications network andcommunications method enabling data transfer between any selectedcommunications nodes by transmitting cell slots on a data path havingplural communications nodes.

2. Description of the Related Art

The data transmission ring network systems which the present inventioncan be applied are the ATMR system and the MARS system.

The ATMR system is a known system and is disclosed in "ATM RING PROTOCOLAND PERFORMANCE" (H. Ohnishi et al. CH2655-9/89/0000-0394 1989 IEEE) orin "Studies in the construction of subscriber-accessible high-speed ringnetworks (ATMR)" (Ito, et al.:Switching Systems Engineering, IEICETechnical Report, SSE 90-41).

The MARS system is a new system (publicly unknown as of Aug. 28, 1992)with a packet transmission ring network format and is invented byTsutomu Tanaka and Hiroshi Yokota who are the co-inventors of thepresent invention and disclosed in Japanese Patent application No.3-107802 (corresponding to U.S. Patent application Ser. No. 07/882608and to Canadian Patent application No. 2,077,027-9) assigned to the sameassignee as the present application.

First, the ATMR system is described below with reference to FIG. 6.

ATMR is a distributed node system with plural access nodes (AN;hereinafter "node") connected in a ring topology by a pair oftransmission paths carrying data in opposite directions. Each accesscell AN is connected with one or more terminals. Data are transmittedand received between terminals by ATMR cell slots circulating around thetransmission ring via ANs. The ATMR cell consists of a binary digitstring having a format shown in FIG. 7. The format is composed of a 12bit access control field (ACF), a 16 bit ring virtual channel number(RVCN) comprising an access node address (ANA) and a logical channelnumber (LCN), 4 bit undefined bits, an 8 bit header check sequence andthe user information of 48 octets carrying the contents of data.

A network controller is connected to one of the access nodes tocontinuously circulate a train of ATMR cell slots around the ring at therate of, e.g., 1400 kilo cell slots per second. Each access node AN hasits own share of cell slots that can be used for sending data from thataccess node to another access node per a predetermined unit time, suchas one second.

In the above example, if there are 70 access nodes and if the share iseven, each access node is permitted to use 20 kilo cell slots persecond. Such a permitted number of cell slots that can be used per aunit time is referred to as a band. Each time an access node uses anempty idle cell slot for sending data from that node to another node, ashare counter provided in that access node is decremented to keep therecord of number of available cell slots that can be used by that accessnode.

If an access node has not used any cell slot for sending data, it is sostated that a window (or windowing size) of that access node is fullyopened. If an access node has used some cell slots within the permittednumber of cell slots, it is so stated that a window is partly closed. Ifan access node has used all the permitted cell slots, i.e., all itsshare, it is so stated that a window is closed.

The access control field (ACF) is needed to make the ATMR systemcompatible with multimedia communications, assuring fair cell access("fairness") between the nodes, and playing a critical role determiningoverall system performance. The ACF will be further described below.

Assuring fairness is achieved by the window size set for each node. Anynode that has used all the permitted cell slots for sending data fromone of the communications terminals, a window of that access node closesto stop further cell transmissions (waives its transmission right) untilall nodes have completed transmitting full window size cells.

According to the ATMR system, the node is either in the active state inwhich the window is still open and there are some data waiting for beingsent, or the inactive state in which the window is closed or the windowis still open but their is no data for sending.

When the node is in the active state, it overwrites its address in theaddress control field (ACF) of the cell slot that passes through thenode. When the node is in the inactive state, the node will notoverwrite its address.

When the node in the inactive state receives a cell slot with itsaddress overwritten in the address control field (ACF), it is understoodthat all the other nodes are in the inactive state. In this case, thenode generates a "reset cell" and, at the same time, initialize thewindow size, and is changed to an hunt state. When the node in the huntstate receives the "reset cell", the cell is changed to unoccupied cell,and the hunt state is cleared.

The window size is also defined according to the different media types,and consumption of the window size is prioritized by communicationsclass so that those cell slots permitting the least delay in the nodeare transmitted first.

FIG. 8 shows each access node which has various functional elements foraccomplishing the access control. The access node has reception ring801, cell reception transfer unit 802, input buffer 803, communicationsterminal 804, plural output buffers 805 provided for each priorityclass, cell transmitting unit 806, cell relay unit 807, state changecontroller 808, and transmission ring 809. The cell relay unit is alsoreferred to as a cell shifting unit.

The cell reception and transfer function is described first. When a cellslot is received from the reception ring 801, the RVCN (ANA+LCN) writtento the cell header is interpreted by the cell reception transfer unit802. If it is determined that the cell slot is addressed to thecommunications terminal 804 connected to that access node AN, the cellslot is input to the input buffer 803 and transferred to thecommunications terminal 804, so that the cell slot is emptied.

The cell relay function is described next. In order to improve the ringutilization rate in an ATMR, the addressed node releases the emptiedcell slot so that any nodes following that addressed node can reuse theemptied cell slot. The cell address is defined in the access nodeaddress (ANA) of the cell header. As a result, when the ANA of thereceived cell slot matches the address of the node to which the cellslot was received, that node empties the cell, but all other nodes(i.e., the unaddressed nodes) will simply throughput the cell to thenext node from the cell relay unit 807. Because the cell slots can bequickly reused in this ATMR system, the total throughput of the networkis improved.

The cell transmission function is described next. Distributed control ofcommunications for all nodes using the access control field information(ACF) in the cell header is used in the ATMR system. Each node providesstate transition processing based on the ACF in the received cell, andthe number of transmission wait-state cells, remaining window size, thecell transmission delay quality assurance timer count and other internalnode states, and the empty base information in the received cell.Transmission of relay cells or transmission wait-state cells over thering is then controlled based on the results of this state transitionprocessing. The cell slots transmitted from the communications terminal804 are then stored in the output buffers 805 in order of priority. Whenthe cell slots can be transmitted as determined by the results returnedfrom the state transition controller 808, they are output to thetransmission ring 809.

In a network environment in which constant bit rate (CBR) data andvariable bit rate (VBR) data are both used, window control and resetcontrol as applied in the ATMR cannot be used to completely control CBRdata due to the intolerance of CBR data transmissions for variations inthe delay time. CBR data is therefore transmitted using cell reservationcommunications method.

Cell reservation communications consists of a cell reservation phase anda cell use phase.

In the cell reservation phase the communications terminal issues arequest to transmit N cell slots of CBR data each time period T, and thenode then reserves N cell slots in time T for the transmitted cellslots. The reservation is made by writing the reservation bit and theaddress of the node making the reservation to the ACF. When the reservedcell slot is emptied by another node to allow reuse, the reservation bitset in the ACF prevents the other nodes from using it, and the cell slotis therefore returned to the node making the reservation. This continuesuntil reservation polling is stopped.

The ATMR is therefore able to distribute band processing according tothe window size assigned to each node, thus maintaining fairness incommunications between nodes.

When the reserved cell comes back around to the node making thereservation, the node recognizes that the cell can be used from thereservation bit set in the ACF and the reserving node address (i.e., itsown address) in the ANA, and then transmits the reservationcommunications cell in the cell use phase.

Next, the MARS system is described. The MARS system employs thestructure shown in FIG. 1.

Plural nodes 103-106 are networked in a ring topology using a pair oftransmissions paths that transmit data in opposite directions. Pluralcommunications terminals may be connected to each node. Fixed lengthcell slots, or train of cells, are sent around the ring.

As shown in FIG. 2, each cell slot comprises a 5-byte header and a48-byte payload area for user data. The 5-byte header contains the nodenumber of the addressee (address of the destination node), and adeclaration bit indicating whether the cell slot is in an idle state,use state, or released state.

It is assumed in the following description that data from one terminal101 is being transmitted to another terminal 102. The transmitted datais processed as a cell of fixed length. To transmit the data, theterminal 101 informs the network controller 107 of the band size neededto transmit the data, and requests ring access (polling). The networkcontroller 107 determines whether the request can be accepted based onthe current state of ring usage, the band capacity already allocated tothe node, and other parameters. If the request is accepted, the networkcontroller 107 assigns the required band capacity to the next node 104.In this manner, the share of the cells for each node is determined, andthe share counter, which is a down counter, is set to the allocatednumber of cells. Each node can transmit data using the cell slotstraveling around the ring according to the assigned band size, i.e.,according to the number of cells allocated to the cell.

The terms "band" and "window" used above for the ATMR system are alsoused for the MARS system. Thus, when the number of cells used by a nodefor transmitting the data is less than the number of cells that can beused as determined by the allocated band, the node window is said to beopened. When the node uses all the cells determined by the allocatedband, the window is said to be closed.

The operation of each part of the node is described below with referenceto FIG. 4.

There are three possible states each cell can take while travelingaround the ring: idle, occupied, and released. These are describedbelow.

(1) Idle state: An idle cell is an empty cell slot which is neitherbeing occupied nor released. When an idle cell slot reaches any nodewith remaining usable band capacity (the window is open), that node canuse the cell slot to transmit data over the ring. For each cell used,the remaining allocated band capacity is decreased by decrementing theshare counter by one.

(2) Occupied: An occupied state cell is a cell currently being used tosend data over the ring. When an occupied cell slot reaches a node, thenode interprets the header to determine the addressed node. If theaddressee is a different node, the cell slot is relayed directlythrough. If the addressee is the present node, the data is extracted andthe emptied cell slot is thereafter treated as an idle cell slot.

(3) Released: A released cell is an empty cell which is released for usein any access node that has a data to be transmitted, and yet effectingno decrement of the share counter in the access node which has used thereleased cell. A released cell is formed as follows. If a node which hasnot used all the share of the allotted cells, but has no data to sendreceives an idle cell slot or occupied state cell but emptied in thatnode, that node writes its own address to the address control field(ACF) in the received cell and, at the same time, it gives an indicationthat the cell is a released cell slot. While the released cell slot iscirculated along the ring network, any access node that has a data to betransmitted can use the released cell slot for sending data to anotheraccess node. In this case, the access node that uses the released cellslot does not decrement the share counter. Thus, even the node with theclosed window can use the released cell slot to send more data.

Referring to FIG. 4, reception buffers 403 and 404 and transmissionbuffers 405 and 406 are respectively provided for the communicationsterminals 401 and 402 connected to the node. The node is connected toother nodes in the network by the reception ring 407 and transmissionring 412.

The cell receiving unit 408 reads the header in each cell slot arrivingfrom the reception ring 407. If the received cell is the occupied cell,and is addressed to a communications terminal connected to that node,the receiving unit 408 extracts the data stored in the payload of thecell slot. The extracted data is input to one of the reception buffers403, 404.

The cell relay unit 409 reads the addressee and the state of the cellslots arriving from the reception ring 407 and performs one of severalconditional operations. Specifically,

(a) if the received cell slot is addressed to that node and is theoccupied cell, the cell slot is reset to an idle state;

(b) if the received cell slot is addressed to another node, it is leftunchanged so that the present state is maintained;

(c) if the received cell slot is the idle cell, the cell slot is leftunchanged;

(d) if the received cell slot is the released cell and is addressed tothat node, the cell slot is returned back to the idle cell; and

(e) if the received cell slot is the released cell, but is addressed toanother node, it is left unchanged in the present state.

The state transition controller 410 determines whether to send out thecell to the transmission ring 412 from the cell relay unit 409 or fromthe cell transmitting unit 411. The cell is sent out to the transmissionring 412 from the cell relay unit 409: (i) when the occupied cell whichis addressed to some other node is received; (ii) when the released celladdressed to some other node is received while having no data to betransmitted; or (iii) when the idle cell is received while the window isclosed. On the other hand, the cell is sent out from the celltransmitting unit 411: (i) when the idle cell is received while thewindow is open (in this case, the sent out cell will be either inoccupied state or in released state); or (ii) when the released celladdressed to some other node is received while having some data to betransmitted.

The operation of the access node shown in FIG. 4 is summarized in atable shown in FIG. 5, in which possible cases under differentconditions (1)-(4) are shown. For the sake of brevity, only a number ofcases in different conditions are explained.

Condition (1): The node condition is such that the window is open andthere are some data in the transmission buffer 405 or 406 waiting forthe transmission.

Case (1-a): The received cell is the occupied cell, and the addressee isto some other node. Thus, no data is extracted. The cell state after thecell relay unit 409 remains the same, i.e., the occupied cell. Thewindow is opened (W>0), meaning that the share to use the cell is stillleft. The queue number Q of data in the buffer 405 or 406 is greaterthan zero, meaning that there are some data in the buffer 405 or 406waiting for the transmission. The cell will be dispatched totransmission ring 412 from the cell relay unit 409. Since the receivedcell is already occupied, this cell can not be used by this node. Thus,the share counter remains unchanged, and also the queue number Q remainsunchanged. The cell sent out from the transmission ring 412 will be inthe occupied state.

Case (1-b): The received cell is the occupied cell, and the addressee isto this node. Thus, data from the cell is extracted so that the cell isemptied. The cell state after the cell relay unit 409 is changed to idlecondition. The window is opened (W>0). The queue number Q of data in thebuffer 405 or 406 is greater than zero, meaning that there are some datain the buffer 405 or 406 waiting for the transmission. The cell will bedispatched to transmission ring 412 from the cell transmitting unit 411.More specifically, the state transition controller 410 outputs a celltransmission command to the cell transmitting unit 411. This commandcauses the cell transmitting unit 411 to read cells from the beginningof the transmission buffer, write them to the cells of the current cellslot, write the addressee node number to the header, and then transmitthe cell slot to the transmission ring 412. The data in the buffer 405or 406 is shifted to the payload area in the cell for the transmission.Thus, the share counter is decremented, and also the queue number Q isdecremented. The cell sent out from the transmission ring 412 will be inthe occupied state.

Case (1-c): The received cell is the idle cell, and the addressee is tothis node. No data extraction takes place. The cell state after the cellrelay unit 409 is maintained to idle condition. The window is opened(W>0). The queue number Q of data in the buffer 405 or 406 is greaterthan zero, meaning that there are some data in the buffer 405 or 406waiting for the transmission. The cell will be dispatched totransmission ring 412 from the cell transmitting unit 411. The data inthe buffer 405 or 406 is shifted to the idle cell for the transmission.Thus, the share counter is decremented, and also the queue number Q isdecremented. The cell sent out from the transmission ring 412 will be inthe occupied state.

Case (1-d): Similar to Case (1-c).

Case (1-e): The received cell is the released cell, and the addressee isto this node. No data extraction takes place. Since the released cellhas made one complete turn in the ring network, the cell state after thecell relay unit 409 is changed to idle condition. The window is opened(W>0). The queue number Q of data in the buffer 405 or 406 is greaterthan zero, meaning that there are some data in the buffer 405 or 406waiting for the transmission. The cell will be dispatched totransmission ring 412 from the cell transmitting unit 411. The data inthe buffer 405 or 406 is shifted to the idle cell for the transmission.Thus, the share counter is decremented, and also the queue number Q isdecremented. The cell sent out from the transmission ring 412 will be inthe occupied state.

Case (1-f): The received cell is the released cell, and the addressee isto some other node. No data extraction takes place. The cell state afterthe cell relay unit 409 is maintained as the released cell. The windowis opened (W>0). The queue number Q of data in the buffer 405 or 406 isgreater than zero, meaning that there are some data in the buffer 405 or406 waiting for the transmission. The cell will be dispatched totransmission ring 412 from the cell transmitting unit 411. The data inthe buffer 405 or 406 is shifted to the released cell for thetransmission. In this case, the share counter will not be decremented,because it has been already decremented in the other node whichgenerated this released cell. The queue number Q is decremented. Thecell sent out from the transmission ring 412 will be in the occupiedstate.

Condition (2): The node condition is such that the window is open, butthere is no data in the transmission buffer 405 or 406.

Case (2-a): The received cell is the occupied cell, and the addressee isto some other node. Thus, no data is extracted. The cell state after thecell relay unit 409 remains the same, i.e., the occupied cell. Thewindow is opened (W>0), meaning that the share to use the cell is stillleft. The queue number Q of data in the buffer 405 or 406 is zero,meaning that there is no data in the buffer 405 or 406. The cell will bedispatched to transmission ring 412 from the cell relay unit 409. Thecell sent out from the transmission ring 412 will be in the occupiedstate.

Case (2-b): The received cell is the occupied cell, and the addressee isto this node. Thus, data from the cell is extracted so that the cell isemptied. The cell state after the cell relay unit 409 is changed to idlecondition. The window is opened (W>0). The queue number Q of data in thebuffer 405 or 406 is zero, meaning that there is no data in the buffer405 or 406. The cell will be dispatched to transmission ring 412 fromthe cell transmitting unit 411. More specifically, the state transitioncontroller 410 outputs a cell transmission command to the celltransmitting unit 411. This command causes the cell transmitting unit411 to set the address of the cell to this node, and to sets the cellslot state to released. Thus, the released cell is sent out from thetransmission ring 412. By this command, the rights to use the cell bythis node are waived, so that the right to use that cell is passed toanother node that has some data to transmit. Since the right to use thecell by this node is waived, the share counter is decremented. The queuenumber Q is maintained zero. The cell sent out from the transmissionring 412 will be in the released state.

Case (2-c): The received cell is the idle cell, and the addressee is tothis node. No data extraction takes place. The cell state after the cellrelay unit 409 is maintained to idle condition. The window is opened(W>0). The queue number Q of data in the buffer 405 or 406 is zero. Thecell will be dispatched to transmission ring 412 from the celltransmitting unit 411. The state transition controller 410 commands celltransmitting unit 411 to make a released cell. The share counter isdecremented, and the queue number Q is maintained zero. The cell sentout from the transmission ring 412 will be in the released state.

Case (2-d): Similar to Case (2-c).

Case (2-e): The received cell is the released cell, and the addressee isto this node. No data extraction takes place. Since the released cellhas made one complete turn in the ring network, the cell state after thecell relay unit 409 is changed to idle condition. The window is opened(W>0). The queue number Q of data in the buffer 405 or 406 is zero. Areleased cell will be dispatched to transmission ring 412 from the celltransmitting unit 411. Thus, the share counter is decremented. The queuenumber Q is maintained zero. The cell sent out from the transmissionring 412 will be in the released state.

Case (2-f): The received cell is the released cell, and the addressee isto some other node. No data extraction takes place. The cell state afterthe cell relay unit 409 is maintained as the released cell. The windowis opened (W>0). The queue number Q of data in the buffer 405 or 406 iszero. The cell will be dispatched to transmission ring 412 from the cellrelay unit 409. The share counter will not be decremented. The queuenumber Q is maintained zero. The cell sent out from the transmissionring 412 will be in the released state.

Condition (3): The node condition is such that the window is closed, butthere are some data in the transmission buffer 405 or 406.

Case (3-a): The received cell is the occupied cell, and the addressee isto some other node. Thus, no data is extracted. The cell state after thecell relay unit 409 remains the same, i.e., the occupied cell. Thewindow is closed (W=0), meaning that the share to use the cell is nomore left. The queue number Q of data in the buffer 405 or 406 isgreater than zero, meaning that there are some data in the buffer 405 or406. The cell will be dispatched to transmission ring 412 from the cellrelay unit 409. The cell sent out from the transmission ring 412 will bein the occupied state.

Case (3-b): The received cell is the occupied cell, and the addressee isto this node. Thus, data from the cell is extracted so that the cell isemptied. The cell state after the cell relay unit 409 is changed to idlecondition. The window is closed (W=0). The queue number Q of data in thebuffer 405 or 406 is greater than zero, meaning that there are some datain the buffer 405 or 406. The cell will be dispatched to transmissionring 412 from the cell relay unit 409. The share counter is maintainedzero, and the queue number Q is maintained Q. The cell sent out from thetransmission ring 412 will be in the idle state.

Case (3-c): The received cell is the idle cell, and the addressee is tothis node. No data extraction takes place. The cell state after the cellrelay unit 409 is maintained to idle condition. The window is closed(W=0). The queue number Q of data in the buffer 405 or 406 is greaterthan zero. The cell will be dispatched to transmission ring 412 from thecell relay unit 409. The share counter is maintained zero, and the queuenumber Q is maintained Q. The cell sent out from the transmission ring412 will be in the idle state.

Case (3-d): Similar to Case (3-c).

Case (3-e): The received cell is the released cell, and the addressee isto this node. No data extraction takes place. Since the released cellhas made one complete turn in the ring network, the cell state after thecell relay unit 409 is changed to idle condition. The window is closed(W=0). The queue number Q of data in the buffer 405 or 406 is greaterthan zero. The idle cell will be dispatched to transmission ring 412from the cell relay unit 409. The share counter is maintained zero andthe queue number Q is maintained to Q. The cell sent out from thetransmission ring 412 will be in the idle state.

Case (3-f): The received cell is the released cell, and the addressee isto some other node. No data extraction takes place. The cell state afterthe cell relay unit 409 is maintained as the released cell. The windowis closed (W=0). The queue number Q of data in the buffer 405 or 406 isgreater than zero so that the data in the buffer 405 or 406 is shiftedto the released cell for the transmission. The cell will be dispatchedto transmission ring 412 from the cell transmitting unit 411. The sharecounter will be maintained zero and, the queue number Q is decremented.The cell sent out from the transmission ring 412 will be in the occupiedstate.

Condition (4): The node condition is such that the window is closed, andthere is no data in the transmission buffer 405 or 406.

Case (4-a): The received cell is the occupied cell, and the addressee isto some other node. Thus, no data is extracted. The cell state after thecell relay unit 409 remains the same, i.e., the occupied cell. Thewindow is closed (W=0), meaning that the share to use the cell is nomore left. The queue number Q of data in the buffer 405 or 406 is zero.The cell will be dispatched to transmission ring 412 from the cell relayunit 409. The cell sent out from the transmission ring 412 will be inthe occupied state.

Case (4-b): The received cell is the occupied cell, and the addressee isto this node. Thus, data from the cell is extracted so that the cell isemptied. The cell state after the cell relay unit 409 is changed to idlecondition. The window is closed (W=0). The queue number Q of data in thebuffer 405 or 406 is zero. The cell will be dispatched to transmissionring 412 from the cell relay unit 409. The share counter is maintainedzero, and the queue number Q is maintained zero. The cell sent out fromthe transmission ring 412 will be in the idle state.

Case (4-c): The received cell is the idle cell, and the addressee is tothis node. No data extraction takes place. The cell state after the cellrelay unit 409 is maintained to idle condition. The window is closed(W=0). The queue number Q of data in the buffer 405 or 406 is zero. Thecell will be dispatched to transmission ring 412 from the cell relayunit 409. The share counter is maintained zero, and the queue number Qis maintained zero. The cell sent out from the transmission ring 412will be in the idle state.

Case (4-d): Similar to Case (4-c).

Case (4-e): The received cell is the released cell, and the addressee isto this node. No data extraction takes place. Since the released cellhas made one complete turn in the ring network, the cell state after thecell relay unit 409 is changed to idle condition. The window is closed(W=0). The queue number Q of data in the buffer 405 or 406 is zero. Theidle cell will be dispatched to transmission ring 412 from the cellrelay unit 409. The share counter is maintained zero and the queuenumber Q is maintained zero. The cell sent out from the transmissionring 412 will be in the idle state.

Case (4-f): The received cell is the released cell, and the addressee isto some other node. No data extraction takes place. The cell state afterthe cell relay unit 409 is maintained as the released cell. The windowis closed (W=0). The queue number Q of data in the buffer 405 or 406 iszero. The cell will be dispatched to transmission ring 412 from the cellrelay unit 409. The share counter will be maintained zero and, the queuenumber Q is maintained zero. The cell sent out from the transmissionring 412 will be in the released state.

Based on the command from the state transition controller 410, the celltransmitting unit 411 reads cells from the beginning of the transmissionbuffers 405 and 406, which are assigned a priority rating. The data tobe transmitted is written in the payload area of the cell slot. Then thecell slot is transmitted to the transmission ring 412.

The operation of the dummy cell generator 413 and cell selector 414 willbe described later together with the error recovery operation.

As described above, according to the MARS system, cells can betransmitted from the transmission buffer using released state cell slotsor the idle cell slots when the window is open. It is thus possible toincrease the cell transmission efficiency, and to avoid deterioration ofcommunications quality resulting from cell loss caused by bufferoverflows, transmission time delays (time-outs), and other factors.

To improve network reliability in the ATMR system, MARS system, or anyother ring network system, two ring transmission paths are used so thatwhen transmission path faults occur, a current-use standby switching ora loop-back control takes place to revive the system until the faultsare mended.

The current-use standby switching is a technique to use a back-uptransmission path when one of the two transmission lines breaks.Normally, only one of the two transmission paths is used and the secondpath is reserved as a back-up transmission path. When an error occurs onthe normally used path, the system is switched to use the back-uptransmission path.

The loop-back control is a technique to use both the normal transmissionpath and the back-up transmission path when a break down takes placebetween two nodes in both of the normal transmission path and theback-up transmission path. When both paths of the ring break downbetween two nodes, the normal transmission path and the back-uptransmission path are mutually connected at said two nodes to establisha ring network so that the communications can be maintained byreflecting the transmission back from the nodes at both ends of thebroken ring.

To prevent even momentary breaks when either current-use standbyswitching or loop-back control is applied in the MARS system, a dummycell generator 413 provided in each node is activated.

Referring again to FIG. 4, the operation of the dummy cell generator 413and cell selector 414 is described below.

When the dummy cell generator 413 is activated, it generates idle cells.When a transmission path error occurs, cells do not reach the cellreceiving means (not shown in the figure) in the reception ring 407. Ifcells are not detected for a predetermined period of time by the cellreceiving means, a control layer unit (also not shown in the figures)determines that a transmission path error have occurred, and generatesan error occurring signal. In response to the error occurring signal,the dummy cell generator 413 is activated to output a dummy cell, andthe cell selector 414 operates thereafter to input the cells generatedby the dummy cell generator 413 to the cell receiving unit 408 and cellrelay unit 409.

The dummy cell is generated with an idle state. When the cell receivingunit 408 detects a dummy cell, it concludes that there are notransmission cells (occupied state cells) from upstream nodes. Thus, allcells generated by the dummy cell generator 413 are input to the cellrelay unit 409. Data can therefore be transmitted from the transmissionbuffer 405, 406 because the cell relay unit 409 treats the dummy cellsas normal idle cells. As a result, even if the transmission path on thereception ring 407 side of the node breaks down, communications betweenthat node and downstream nodes, as well as any nodes not connectedthrough the interrupted transmission path, can be maintained.

The ATMR system and MARS system have their own superiorities andinferiorities.

According to the ATMR system, it provides a high level of fairness andattains a high throughput rate. However, there are also some problems inthe ATMR system.

Consider the case in which no data is sent from any of the nodes in theATMR system. The cells traveling around the ring are either empty orreset cells. If suddenly data transmission is started from one of thenodes (e.g., node M), that node can send data continuously up to thewindow size. Since all cells output from node M will be occupied statecells, no usable cells will pass the nodes between node M and thedestination (addressee) node once the node M begins transmission. Thismeans, of course, that no node between the sending and receiving nodeswill be able to send data over the network. Transmission is thereforeforced to wait while the node M transmission is in progress, and thetransmission delay increases. Once the node M transmission ends,priority will pass to the node closest to node M, and the fairnessbetween nodes will not be maintained.

As also described, cell reservation communications is introduced tomixed CBR and VBR data networks under ATMR to maintain CBR datatransmission integrity. With this format, however, a cell reservationphase is required after network polling before actual data transmissioncan begin. This phase also has the potential for increasing the celltransmission delay time. In addition, because the reserved cells cannotbe used by any other node, the utilization rate of the network may alsodrop.

According to the MARS system, a released state cell slot is introducedso that the nodes negotiate for use of the unoccupied portion of theband allotted to each node, effectively increasing the utilization rateof the ring and improving the cell transmission delay time. However, thefollowing problems are also presented in the MARS system.

Specifically, the released state cell slots can be used freely by any ofthe nodes. In other words, (1) a node that has consumed its allottedband but still has data to send can use the released state cell slots tocontinue transmission, and (2) any node that has not used its allottedband can also use the released state cell slots to send data withoutusing its own allotted band.

In other words, the MARS system is optimized for compatibility withcommunications (connection-oriented communications) in which accesspolling precedes data sending and uses band allocation. In this type ofring network, however, it is also necessary to assure sufficientconsideration for communications between computers and otherconnectionless communications. In connectionless communications, data isnot transmitted at any regular cycle, large volumes of data are producedin a short period of time (burst communications), and polling does notprecede the start of data transmission. If connectionless communicationsis accommodated in the MARS system, a certain band capacity could beallocated to the node. Connectionless data is generated at sudden,unpredictable times, however, temporarily using a large number ofreleased state cell slots and possibly disrupting distributed managementof the band capacity between nodes.

Errors could therefore be introduced to connection-orientedcommunications, and the quality required for the different transmissionmodes may not be maintained.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide a ringnetwork that assures fairness between nodes, increases the utilizationrate of the overall system and transmits data efficiently, and caneasily adapt to faults in the network in a mixed CBR/VBR dataenvironment enabling both connection-oriented and connectionlesscommunications.

To achieve this object, a packet communications network for transmittingdata between nodes by the use of cell slots circulating the networkcomprises: plural nodes connected in a ring network; a networkcontroller connected to one of the nodes for allocating the number ofusable cell slots per unit time to each node; center node inserted inthe ring network for sequentially generating, at a selected rate, firstand second types of cell slots for transmitting first and second typesof data, respectively, each cell slot having a type code for identifyingeither one of the first and second types, and a status code foridentifying, when the cell slot is the first type, any one of an idlestate, an occupied state and a released state, and for identifying, whenthe cell slot is the second type, either the cell is an unoccupied cell,occupied cell or a reset cell; and each of the plural nodes comprising:address detection means for detecting whether the addressee is to thereceived node or to any other node; type detection means for detectingwhether the received cell is the first type or the second type; statusdetection means for detecting, when the received cell is the first type,whether the received cell is in the idle state, the occupied state orthe released state, and for detecting, when the received cell is thesecond type, whether the received cell is the unoccupied cell, theoccupied cell or the reset cell; data putting means for putting, whenthe received cell is the first type, data on the cell slot which is ineither one of the idle state and released state, and for putting, whenthe received cell is the second type, data on the unoccupied cell slot;status transition means for changing, when the received cell is thefirst type, the status of the received cell from idle to occupied if thenode puts data to the received cell, from idle to released if the nodewaives its right to use the cell slot, or from released to idle if thereleased cell makes one complete turn around the ring network withoutbeing used by other nodes.

According to a preferred embodiment, in the packet communicationsnetwork, each of the plural nodes further comprises first buffer meansfor storing first type data to be transmitted by the first type cellsand second buffer means for storing second type data to be transmittedby the second type cells.

According to a preferred embodiment, in the packet communicationsnetwork, the first type data is a connection-oriented data, and thesecond type data is a connectionless data.

According to a preferred embodiment, the packet communications networkfurther comprises dummy cell generating means for sequentiallygenerating, at the selected rate, the first and second types of cellslots when a network transmission path fault occurs in a path upstreamof the node.

According to a preferred embodiment, in the packet communicationsnetwork, the dummy cell generating means generates the first type cellslots in the idle status, and the second type cell slots in a repetitionof one reset cell and a predetermined number of unoccupied cells, andthe first type cell slots and the second type cell slots beinginterleaved in a predetermined ratio.

According to a preferred embodiment, in the packet communicationsnetwork, the ring is doubled.

Furthermore, according to the present invention, a method fortransmitting data between nodes in a packet communications network bythe use of cell slots circulating the network comprises the step of:sequentially generating from the center node at a selected rate, firstand second types of cell slots for transmitting first and second typesof data, respectively, each cell slot having a type code for identifyingeither one of the first and second types, and a status code foridentifying, when the cell slot is the first type, any one of an idlestate, an occupied state and a released state, and for identifying, whenthe cell slot is the second type, either the cell is an unoccupied cell,an occupied cell or a reset cell; and in each of the plural nodes, themethod comprises: detecting whether the addressee is to the receivednode or to any other node; detecting whether the received cell is thefirst type or the second type; detecting, when the received cell is thefirst type, whether the received cell is in the idle state; the occupiedstate or the released state; detecting, when the received cell is thesecond type, whether the received cell is the unoccupied cell, theoccupied cell or the reset cell; putting, when the received cell is thefirst type, data on the cell slot which is in either one of the idlestate and released state; putting, when the received cell is the secondtype, data on the unoccupied cell slot; and changing, when the receivedcell is the first type, the status of the received cell from idle tooccupied if the node puts data to the received cell, from idle toreleased if the node waives its right to use the cell slot, or fromreleased to idle if the released cell makes one complete turn around thering network without being used by other nodes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given below and the accompanying diagrams wherein:

FIG. 1 is a diagram of the network topology according to the presentinvention; .

FIG. 2 is a drawing of the cell slot structure according to the presentinvention;

FIG. 3 is a block diagram of the node functions according to thepreferred embodiment of the present invention,

FIG. 4 is a block diagram of the node functions according to the MARSsystem;

FIG. 5 is a table used to describe the ring access operation of the MARSsystem;

FIG. 6 is a diagram of a conventional ATMR network topology;

FIG. 7 is a drawing of the ATMR cell structure; and

FIG. 8 is a block diagram of the node functions according to theconventional ATMR network.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment of a ring network and packet communicationsmethod according to the present invention is described below withreference to the accompanying figures. The structure of the ring networkis described first with reference to FIG. 1.

This network comprises a network controller 107 and communicationsterminals 101 and 102 connected to network nodes 103-106. The networkcontroller 107 controls the bands and other aspects of the ring network.Fixed-length cell slots (packets) travel the transmission paths linkingthe nodes 103-106. Data from any of the nodes is transmitted using thesecell slots. According to the present invention, the ring network acceptstwo types of cell slots: the first type (type 1) is for sendingconnection-oriented data which requires a call setting beforecommunications begins; and the second type (type 2) is for sendingconnectionless data such as used for sending data between computers.

Referring to FIG. 2, each cell slot has a header in which a general flowcontrol area comprising four bits (b1, b2, b3, b4) is provided. In thefour bit area, bit b3 is used as a type bit for identifying the type ofthe cell slot. When the type bit is "0", it identifies that the cellslot is the type 1, and when it is "1", the cell slot is the type 2.Bits b2 and b1 are used for identifying the status of the cell slot. Asto type 1 cell, when (b2, b1)=(0,0), it is indicated that the cell is inthe idle state, when (b2, b1)=(0,1), in the release state, and when (b2,b1)=(1, *), in the occupied state, in which * can be either "0" or "1".As to type 2 cell, when (b2, b1)=(0,0), it is indicated that the cell isin unoccupied state, when (b2, b1)=(1,0), in the occupied state, andwhen (b2, b1)=(*, 1), the cell is the reset cell.

The use of the three states (occupied, released, or idle) has beendescribed with relation to the conventional MARS network above, andfurther description is omitted below. The cell slot type is furtherdescribed below.

The network controller 107 can allocate the available band capacity onthe ring by type using the declaration bits provided in the cell slotheaders as described above. Data output to the network from thecommunications terminal is written selectively to cell slots of therequired type. As described above, there are two cell slot types: type 1for connection-oriented data requiring call setting beforecommunications begins; and type 2 for connectionless data such as usedfor sending data between computers.

When transmitting data from communications terminal 101 tocommunications terminal 102, parameters indicating, for example, theband capacity required for transmission are sent to the networkcontroller 107 before data transfer begins when the data being sent isconnection-oriented data. The network controller 107 accepts or deniesthe access request based on the current network status, including thepreviously accepted access requests and network traffic, and the currentrequest value. If accepted, the network controller 107 allocates therequired band capacity to the node. Since the request in this case isfor type 1 data, type 1 cell slots are used for data transmission. It isto be noted that this method of accessing the ring when sendingconnection-oriented data from a node to the ring is the MARS systemwhich is fully disclosed in Japanese Patent application No. 3-107802(corresponding to U.S. patent application Ser. No. 07/882608 and toCanadian Patent application No. 2,077,029-9) assigned to the sameassignee as the present application. The disclosure in Japanese Patentapplication No. 3-107802 (corresponding to U.S. patent application Ser.No. 07/882608 and to Canadian Patent application No. 2,077,027- 9) isforming a part of this specification.

In connectionless communications the band used for data transmission ispre-allocated in a fixed amount for each node, and each node can use itsallocated capacity freely as needed. Type 2 cell slots are used to senddata over the ring in this case, but the ring is accessed using theconventional ATMR method described above. It is to be noted that theband capacity allocated for connectionless data transmission for eachnode and the proportion between the band allocated for each type on thering can be changed after the network is in service.

The structure of each node is described below with reference to FIG. 3.Plural communications terminals 301 and 302 are connected to the nodeshown, and reception buffers 303 and 304 are provided for the terminals,respectively. First transmission buffers 305 and 306 are provided forthe type 1 data, and a second transmission buffer 307 is provided forthe type 2 data. In the preferred embodiment of the invention the firsttransmission buffer 305 for type 1 data is for the high quality datatransmission, and the buffer 306 for type 1 data is for the normalquality data transmission. The nodes are linked by a reception ring 308and transmission ring 313, and further comprise a cell receiving unit309, cell relay unit 310, state transition controller 311, celltransmitting unit 312, dummy cell generator 314, and cell selector 315.The state transition controller 311 is coupled with a type detector 320for detecting the type of the received cell, whether it is type 1 ortype 2. Also, the dummy cell generator 314 is coupled with an occurrenceratio setting unit 321 for setting an occurrence ratio of type 1 celland type 2 cell. Furthermore, particularly in the center node 104 whichis connected with the network controller 107, an occurrence ratiosetting unit 322 for setting an occurrence ratio of type 1 cell and type2 cell is provided. Thus, the type 1 cells and type 2 cells are passedaround the network in an interleaved manner at a predetermined ratiodetermined by the ratio setting unit 322. The operation of the dummycell generator 314 and cell selector 315 will be described with specificrelation to the loop-back operation of the network.

Transmission of type 1 data is described first. The type 1 data outputfrom the communications terminal 301 or 302 is stored in the firsttransmission buffer 305 or 306 according to the priority class of thedata. The MARS system described above is used to access the ring andsend the data from the buffer to the cell slots on the ring, and furtherdescription is omitted below. It should be noted, however, that onlytype 1 cell slots are accessed on the ring.

Control of the connection-oriented data (type 1) band allocated by thenetwork controller 107 shown in FIG. 1 is described next.

This control is provided by the state transition controller 311. Theband is defined as the number of cell slots guaranteed for use dividedby the number of cell slots on the ring passing during a measured periodof time. The transmission rate of the ring in this embodiment isapproximately 1.4M cells/sec. If the total allocation for one node is aband of 20 k cells/sec. for the internally connected terminals, the bandallocation is 20/1400 if the measured cycle is 1 k cells/sec., whichmeans that the node can use 20 of 1400 cells passing in a predeterminedmeasured period. Whether these 20 cells are used intermittently (that isin cyclically) or intensely (that is in burst) is left to the nodecontrol. By defining the measured cycle differently for each node, theuse of cell slots on the ring is randomized.

Transmission of connectionless data (type 2) is described next.

Connectionless data output from the communications terminal 301 or 302is stored in the second transmission buffer 307 of the node. Type 2 cellslots arriving at the node from the reception ring 308 are used to sendcells from the second transmission buffer 307 to the ring. The windowcontrol and reset control protocols of the ATMR system as describedabove are used for ring access; cell reservation communications is notused.

It is to be noted that by the network controller 107, type 1 cells andtype 2 cells are passed around the ring network in a predeterminedsequence depending on the requirements from various nodes.

Operation of the dummy cell generator 314 and cell selector 315 isdescribed next.

The dummy cell generator 314 retains the patterns for both type 1 andtype 2 cell patterns, and generates idle state type 1 cells and eitherreset or unoccupied state type 2 cells. The dummy cells are generated asreset cells at each normal reset cycle, and unoccupied cells aregenerated at all other times. When a fault in the transmission path isdetected by the data receiver (not shown in FIG. 1) on the receptionring 308, the cell selector 315 selects the dummy cell generator 314 togenerate cells.

When dummy cells are produced, the cell receiving unit 309 determinesthat there are transmission cells (unoccupied state cell slots) from anyupstream nodes, forwards cells to the cell relay 310, and outputs datafrom the transmission buffers 305 or 306. It is therefore possible tomaintain communications between this node and downstream nodes even whena transmission path fault occurs on the reception ring 308 side of thenode. It is to be noted that the dummy cell generator 314 and cellselector 315 provided separately in the preferred embodiment of theinvention can also be integrated to a single unit.

As thus described, the present invention defines three states for thecell slots traveling the ring, and uses the released state cell slots inparticular to negotiate use of the band between nodes. The cell slots onthe ring can therefore be more efficiently used for data transmission,and the transmission delay time can be reduced. In a mixed CBR and VBRdata environment, CBR data is also protected from the effects of bursttransmission of VBR data.

Cell slots are also defined as one of two types. The band capacity isallocated for connectionless data transmissions between computers, andconnection-oriented data transmission, and both the ring access methodand transmission buffers are used according to the data type. As aresult, the effects of non-cyclical, high burst connectionless datatransmissions on other network traffic is eliminated for more efficientoverall network performance.

Furthermore, because a dummy cell generator in each node generates dummycells when a transmission path fault occurs, cells affected by thetransmission path fault are not throughput, and communications can bemaintained between nodes not linked directly through the fault. Inaddition, the proportion between cell types allocated for the band canbe maintained when a fault occurs and loop-back control is implementedby programming the dummy cell generator to produce type 1 and type 2cells in the same proportion as the cells traveling on the ring.

As described hereinabove, the utilization rate of the ring can beincreased by setting the cell slots traveling around the ring to one ofthree states. In a mixed CBR data and VBR data environment, the affectsof the transmission characteristics of one data type on the other can beavoided, and the data transmission delay time can be reduced. Inaddition, by allocating the band used by connection-oriented data andconnectionless data, and using different ring access systems for eachdata type, transmission of each data type can be prevented fromaffecting the other. As a result, data can be transmitted over thenetwork according to the traffic characteristics of differing datatypes.

Furthermore, when a transmission path fault occurs and loop-back controlor another control method is implemented to maintain communicationsbetween unaffected nodes, communication of type 1 and type 2 data can bemaintained by programming the dummy cell generator to output type 1 andtype 2 dummy cells in the same proportion as that of the ring before thetransmission path fault occurred.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A packet communications network transmitting databetween nodes by the use of a plurality of cell slots circulating thenetwork, the network being characterized by a bandwidth, the networkcomprising:a plurality of nodes connected in a ring network; a networkcontroller connected to one of said nodes for allocating one of aplurality of portions of said bandwidth to each of said nodes; a centernode inserted in said ring network for sequentially generating, at aselected rate, first and second types of cell slots for transmittingfirst and second types of data, respectively, each of said cell slotsincluding a type code identifying said cell slot as being associatedwith one of said first and second types of data, each of said cell slotsincluding a status code defined for use according to a first ring accesssystem when said cell slot is associated with said first type of dataand defined for use according to a second ring access system when saidcell slot is associated with said second type of data; each of saidplurality of nodes comprising:address detection means for detectingwhether a node receiving a cell slot is an addressee node; typedetection means for detecting whether said received cell slot isassociated with said first data type or said second data type; statusdetection means for detecting said status code of said received cellslot; data putting means for putting data on said received cell slotaccording to said first ring access system when said received cell slotis of said first data type and according to said second ring accesssystem when said received cell slot is of said second data type; andstatus transition means for changing said status code of said receivedcell according to said ring first access system when said received cellis of said first data type and according to said second ring accesssystem when said received cell slot is of said second data type.
 2. Thepacket communications network of claim 1, wherein said status detectionmeans detects whether said received cell slot is in an idle state, anoccupied state or a released state in accordance with said first ringaccess system when said received cell slot is of said first data type,and whether said received cell slot is an unoccupied cell, an occupiedcell or a reset cell in accordance with said second ring access systemwhen said received cell slot is of said second data type.
 3. The packetcommunications network of claim 2, wherein said data putting means putsdata on said received cell slot which is either in said idle state orsaid released state in accordance with said first ring access systemwhen said received cell slot is of said first data type, and on saidunoccupied cell in accordance with said second ring access system whensaid received cell slot is of said second data type.
 4. The packetcommunications network of claim 2, wherein said status transition meanschanges, in accordance with said first ring access system when saidreceived cell slot is of said first type, said received cell slot'sstatus code from said idle status to said occupied status if said nodereceiving said received cell slot puts data to said received cell slot,from said idle status to said released status if said node receivingsaid received cell slot waives its right to use said node receiving saidreceived cell slot, or from said released state to said idle status ifsaid received cell made one complete turn around said ring with saidreleased status without being used by said other nodes.
 5. The packetcommunications network of claim 1 further comprising dummy cellgenerating means for sequentially generating, at said selected rate,said first and second types of cell slots when a network transmissionpath fault occurs in a path upstream of said node receiving saidreceived cell slot.
 6. The packet communications network of claim 5,wherein said dummy cell generating means generates said first type cellslots in said idle status and said second type cell slots in arepetition of one of said reset cells and a predetermined number of saidunoccupied cells, said first and second type cell slots beinginterleaved in a predetermined ratio.
 7. A packet communications networkfor transmitting data between nodes by the use of cell slots circulatingthe network comprising:plural nodes connected in a ring network; anetwork controller connected to one of said nodes for allocating thenumber of usable cell slots per unit time to each node; a center nodeinserted in said ring network for sequentially generating, at a selectedrate, first and second types of cell slots for transmitting first andsecond types of data, respectively, each cell slot having a type codefor identifying either one of said first and second types, and a statuscode for identifying, when the cell slot is the first type, any one ofan idle state, an occupied state and a released state, and foridentifying, when the cell slot is the second type, either the cell isan unoccupied cell, occupied cell or a reset cell; each of said pluralnodes comprising:address detection means for detecting whether anaddressee node is a receiving node or any other node; type detectionmeans for detecting whether a received cell is the first type or thesecond type; status detection means for detecting, when the receivedcell is the first type, whether the received cell is in the idle state,the occupied state or the released state, and for detecting, when thereceived cell is the second type, whether the received cell is theunoccupied cell, the occupied cell or the reset cell; data putting meansfor putting, when the received cell is the first type, data on the cellslot which is in either one of the idle state and released state, andfor putting, when the received cell is the second type, data on theunoccupied cell slot; and status transition means for changing, when thereceived cell is the first type, the status of the received cell fromidle to occupied if the node puts data to the received cell, from idleto released if the node waives its right to use the cell slot, or fromreleased to idle if the released cell makes one complete turn around thering network without being used by other nodes; and dummy cellgenerating means connected to the ring network for sequentiallygenerating, at said selected rate, said first and second types of cellslots when a network transmission path fault occurs in a path upstreamof said dummy cell generating means.
 8. A packet communications networkfor transmitting data between nodes by the use of cell slots circulatingthe network comprising:plural nodes connected in a ring network; anetwork controller connected to one of said nodes for allocating thenumber of usable cell slots per unit time to each node; a center nodeinserted in said ring network for sequentially generating, at a selectedrate, first and second types of cell slots for transmitting first andsecond types of data, respectively, each cell slot having a type codefor identifying either one of said first and second types, and a statuscode for identifying, when the cell slot is the first type, any one ofan idle state, an occupied state and a released state, and foridentifying, when the cell slot is the second type, either the cell isan unoccupied cell, occupied cell or a reset cell; each of said pluralnodes comprising:address detection means for detecting whether anaddressee node is a receiving node or any other node; type detectionmeans for detecting whether a received cell is the first type or thesecond type; status detection means for detecting, when the receivedcell is the first type, whether the received cell is in the idle state,the occupied state or the released state, and for detecting, when thereceived cell is the second type, whether the received cell is theunoccupied cell, the occupied cell or the reset cell; data putting meansfor putting, when the received cell is the first type, data on the cellslot which is in either one of the idle state and released state, andfor putting, when the received cell is the second type, data on theunoccupied cell slot; and status transition means for changing, when thereceived cell is the first type, the status of the received cell fromidle to occupied if the node puts data to the received cell, from idleto released if the node waives its right to use the cell slot, or fromreleased to idle if the released cell makes one complete turn around thering network without being used by other nodes; and dummy cellgenerating means for sequentially generating, at said selected rate,said first and second types of cell slots when a network transmissionpath fault occurs in a path upstream of said node.
 9. The packetcommunications network of claim 8, wherein each of said plural nodesfurther comprises first buffer means for storing first type data to betransmitted by the first type cells and second buffer means for storingsecond type data to be transmitted by the second type cells.
 10. Thepacket communications network of claim 8, wherein said first type datais a connection-oriented data, and said second type data is aconnectionless data.
 11. The packet communications network of claim 8,wherein said dummy cell generating means generates the first type cellslots in the idle status, and the second type cell slots in a repetitionof one reset cell and a predetermined number of unoccupied cells, andsaid receiving first type cell slots and said second type cell slotsbeing interleaved in a predetermined ratio.
 12. The packetcommunications network as claimed in claim 8, wherein said ring networkis doubled.